The present invention relates to a method and apparatus for recording information in an information recording medium by radiation of an energy beam, or more in particular to an information recording method very effective for a phase change optical disk and an information recording apparatus using such an information recording method.
A conventional method of recording and erasing information in a rewritable record film is disclosed, for example, in JP-A-62-175948 (laid open Aug. 1, 1987), which uses a magneto-optical disk of an exchange couple double-layered film as a record film. Another conventional method for recording and erasing information in a rewritable record film is disclosed in JP-A-62-259229 (laid open Nov. 11, 1987), which uses a record film for a phase change optical disk capable of high-speed erasure by crystallization within substantially the same time as the laser radiation time for recording. In these cases, the power of an energy beam is alternated between at least two levels both higher than the read level, i.e. between at least a high power level and an intermediate power level. This method has the advantage that what is called xe2x80x9coverwritexe2x80x9d is possible with new information recorded while at the same time erasing the existing one. Also, as disclosed in JP-A-62-259229 described above and JP-A-3-185629 (laid open Aug. 13, 1991), a record mark can be prevented from assuming a shape such that the rear portion of the record mark is wider than the front portion thereof by changing the energy beam between three levels including a high power level, an intermediate level and a power level lower than the intermediate level.
Research is under way for increasing the density of a rewritable digital video disk (DVD-RAM) using a phase change record film. In an optical disk device for performing the mark edge recording in a phase change record film such as the DVD-RAM, substantially the same temperature and substantially the same cooling rate are required for recording at every part of the outer edge where the record film is melted for forming a record mark or a mark portion in order to prevent a mark shape distortion and residue. The various record waveforms thus far known, however, fail to meet these conditions sufficiently and the feasible recording density is limited. Especially with the DVD-RAM having a recording capacity of 4.7 GB or more, the distance between centers of laser beams radiated onto a recording medium to form adjacent two mark portions thereon is small as compared with the diameter of the laser beam spot, with the result that light is considerably overlapped in distribution. It is necessary to prevent a record mark distortion caused by this phenomenon. In the case where the space portion between mark portions is short, the record mark edge position of a reproduced signal waveform shifts due to the fact that such mark portions cannot be resolved by the beam spot. This inconvenience is also required to be prevented.
With the increase in digital signal processing rate in recent years, demand has been rising for an increased recording and reproduction rate of an information recording apparatus. In order to meet this demand, a higher relative speed between an energy beam and an information recording medium has become crucial. Therefore, an information recording method is required which is capable of performing a stable recording operation even in the case where the relative speed between an energy beam and an information recording medium is high.
The object of the present invention is to provide an information recording method and apparatus capable of recording information with high density.
The invention is suitable for recording information accurately in the case where the recording density is high and/or the relative speed between an energy beam and an information recording medium is high.
On the other hand, a technique for reducing the track pitches is under development with the intention of increasing the recording density. A method exists, for example, in which information is recorded in both grooves and lands (areas between grooves) formed on an information recording medium. According to this method, crosstalks of reproduced signals from lands to grooves or from grooves to lands can be cancelled by setting the grooves to a proper depth (optical phase difference between lands and grooves).
The heat generated by the energy beam is used for recording information. Therefore, thermal interferences occur to adjacent tracks (grooves adjacent to lands or lands adjacent to grooves) in the case where the energy beam position cannot be controlled in stable fashion. This leads to the problem that the information recorded in adjacent tracks is erased.
The present invention is suitable for recording information accurately without erasing the information in adjacent tracks even in the case where the information is recorded in an information recording medium having narrow track pitches or especially an information recording medium corresponding to the land/groove recording scheme and in the case where the track pitches are not more than the diameter of the recording energy beam.
Another crucial problem is how to improve the recording sensitivity. Normally, with the increase in relative speed between the information recording medium and the energy beam, the energy beam passes a record mark on the information recording medium within a shorter time. Thus, the amount of energy radiated on the information recording medium in a unit time is reduced, and therefore the portion of the record film to be formed with a record mark is often insufficiently heated. Also, accurate recording, which can be accomplished with pulses of very narrow width, requires a high peak laser power.
The present invention is also suitable for recording information accurately without a large energy beam power in the case where the relative speed between the information recording medium and the recording energy beam is increased and/or in the case where information is recorded in an information recording medium liable to be cooled rapidly.
According to one aspect of the invention, there is provided a method of recording information in a recording medium capable of being set in a first state of a second power level and in a second state of a third power level higher than the second power level of an energy beam, in which the energy beam is radiated while moving the energy beam and the recording medium relatively to each other and information in terms of the length and interval of mark portions in the second state is recorded in the recording medium, the method comprising the first step of irradiating the recording medium with an energy beam of a first power level lower than the second and third power levels before and/or after recording the information, the second step of irradiating the recording medium with at least one pulse of one or more energy beam pulses of the third power level for forming a mark portion in the second state, and the third step of irradiating the recording medium, before or after the first pulse of one or more energy beam pulses for forming the mark portion, with an energy beam pulse of a radiation energy larger in the case where the mark portion in the second state has a first length than in the case where the mark portion in the second state has a second length.
In the above-mentioned method, the third step can be replaced by an equivalent third step of, in the case where the space portion following a mark portion in the second state has a first length, irradiating the recording medium, after the last pulse of one or more energy beam pulses for forming the mark portion, with an energy beam pulse having an energy smaller than in the case where the space portion has a second length and at a power level lower than the second power level.
In the last-mentioned method, the two third steps can of course be employed at the same time.
According to another aspect of the present invention, there is provided a method of recording information in the form of space and mark portions on a recording medium capable of assuming first and second physical states corresponding to space and mark portions of information, respectively, the recording medium being irradiated, to produce a length of a portion of the recording medium in the second physical state, with an energy beam being movable relative to the recording medium and being modulated to have power levels varying with time in a pulse waveform in accordance with a mark portion of information, wherein:
the pulse waveform includes an information pulse section having at least one pulse serving to form a second physical state recording medium portion and a mark edge adjusting pulse section continuous with the information pulse section, the mark edge adjusting pulse section being cooperative with the information pulse section to define the length of the second physical state recording medium portion to be produced.
According to still another aspect of the invention, there is provided an apparatus for recording information in a recording medium capable being set in a first state of a second power level and in a second state of a third power level higher than the second power level of an energy beam, the apparatus comprising an energy beam radiation means and means for moving the energy beam and the recording medium relative to each other, the information being recorded on the recording medium in the form of length and space of a mark portion in the second state, wherein the energy beam radiation means includes a waveform generating circuit having first means for irradiating the recording medium with a beam of a first power level (P1) lower than the second and third power levels before and/or after recording the information, second means for irradiating the recording medium with at least a pulse of one or more energy beam pulses of the third power level for forming a mark portion in the second state, and third means for increasing the radiation energy in the case where the mark portion in the second state has a first length as compared with when said mark portion in said second state has a second length, before or after the first pulse of one or more energy beam pulses for forming the mark portion.
According to yet another aspect of the invention, there is provided an apparatus for recording information in a recording medium capable of being set in a first state of a second power level and in a second state of a third power level higher than the second power level of an energy beam, comprising energy beam radiation means and means for moving the energy beam and the recording medium relative to each other, the information being recorded on the recording medium in the form of length and interval of a mark portion in the second state, wherein the energy beam radiation means includes a waveform generating circuit having first means for irradiating the recording medium with a beam of a first power level (P1) lower than the second and third power levels before and/or after recording the information, second means for irradiating the recording medium with at least a pulse of one or more energy beam pulses of the third power level for forming a mark portion in the second state, and third means for irradiating the recording medium, in the case where the space portion after a mark portion in the second state has a first length, with an energy smaller than when the space portion following the mark portion has a second length, at a power level lower than the second power level after the last pulse of one or more energy beam pulses for forming the mark portion.
In this specification, at least an energy beam pulse train for forming a mark portion is defined as a train of pulses for forming a mark portion arranged substantially equidistantly with a shorter interval than the channel clock in the recording apparatus.